Flotation method and reagent



Patented Feb. 16, 1954 UNITED STATES PATENT OFFICE to United States tionof New Jersey Steel Corporation, a corpora- N Drawing. Application July5, 1950, Serial No. 172,197

7 Claims.

This invention relates to improved methods for flotation of iron oxideminerals from silicious minerals and to improved flotation reagents. Asused herein, the term iron oxide minerals illcludes hydrated oxides,such as the various limomites and goethite, as well as hematite andmagnetite. The term silicious minerals includes quartz and varioussilicates, such as feldspar.

The flotation methods of the present invention are particularlyapplicable for beneficiating lowgrade iron ores, such as taconites ofthe Mesabi range. Taconites vary greatly in physical structure andchemical composition. Previously known flotation methods can make afairly satisfactory separation between the iron oxide and the siliciouscomponents in some grades of taconite, but in most instances theyrequire relatively expensive reagents and they float the siliciousminerals and direct the iron oxide minerals to the underflow. Forpractical operation, it would be essential to employ inexpensivereagents, such as collectors of the fatty acid type, and it would bedesirable to float the iron oxide minerals, since they are lessvoluminous than the silicious minerals and it is easier to recover themwhen they are a float product than when they are dispersed as anunderflow product. Although it is known that collectors of the fattyacid type are capable of floating iron oxide minerals, they have notbeen used to any extent for this purpose because with previously knownmethods they do not generally furnish clear separations of the ironoxide minerals from the silicious minerals.

An object of the present invention is to provide improved flotationmethods which utilize relatively inexpensive reagents and yet furnish asatisfactory separation between iron oxide minerals and siliciousminerals, and which can be applied to some ores that previously havebeen difficult to beneficiate, and which float iron oxide minerals anddirect silicious minerals to the underflow.

A further object of the invention is to provide flotation methods whichutilize relatively inexpensive cellectors of the fatty acid type forfloating iron oxide minerals, in conjunction with an improved agent forwetting and thereby depressing silicious minerals, namely colloidalsilica which hasv a mol ratio of silica to alkali metals of at least 25to l.

A further object of the invention is to provide improved preparedflotation reagents which consist of an emulsion of a collector of thefatty acid type and colloidal silica which has a mol ratio of silica toalkali metals of at least 25 to 1, and preferably having a pH value of 3to 6 to promote stability.

I define the term collectors of the fatty acid type as used herein toinclude higher fatty acids, such as oleic acid, palmitic acid, linoleicacid, linolenic acid, lauric acid, myristic acid, stearic acid, andtariric acid; esters of the higher fatty acids, such as their glyceryland glycol esters; resin acids, such as abietic acid; and naphthenicacids; and various mixtures of the foregoing, but in each instance beingsubstantially free of ions of alkali metals such as would be found inthe sodium soap of the various acids; Practically I prefer crudemixtures of fatty acids and resin acids, such as tall oil, because suchmixtures are readily available at low cost, for example, under the tradenames Opoil and Facoil."

For the successful practice of the present in.- vention, it is essentialthat the reagents have a very low content of ions of alkali metals andalkaline earth metals, although appreciable amounts of the latter oftenoccur in the ore. It

7 would be desirable that such ions be absent entirely, since theyweaken the Wetting action of colloidal silica on particles of siliciousminerals. It is known that alkaline earth metal ions, such as calciumions, tend to activate silicious minerals and to cause fatty acidcollectors to float them. The colloidal silica Wetting agent mustovercome this tendency. Practically it is difficult to obtain reagentsthat are entirely free of such ions and I find that certain smallamounts can be tolerated. Therefore the mol ratio of silica to alkalimetals should be at least 25 to 1.

The colloidal silica which I employ can be prepared by neutralizingcommercial sodium silicate with an acid, such as sulphuric acid, usingconcentrations that form a gel, and then washing out the sodium salt.Another way is by treating sodium silicate with an medium which replacesthe sodium ions of the silicate with hydrogen ions. The resultingcolloidal silica in the first instance is a gel and in the secondinstance a sol. The silica gel remains effective for my purpose if it isdried at moderate temperatures (e. g. C.) and ground. A suitablecolloidal silica is available commercially under the trade name Ludcx.The analysis of this commercial material as furnished by the producer isas follows:

SiOz 29 to 31%.

Since methods of preparing such material are known and per se are notpart of the presentacid type ion exchangeinvention, no more detaileddescription is believed necessary.

A preferred Way of practicing the present invention is to pre-mix areagent which consists of a collector of the fatty acid type andcclioidal silica which has a mol ratio of silica to alkali metals of atleast 25 to l. The colloidal silica functions as an emulsifying agentfor the collector. The ratio of colloidal silica solution ofapproximately 30% S102 content to collector can vary from about 0.2 to2.0 parts by weight of aqueous colloidal silica solution to one part byweight of collector. I find a ratio of about 1 to 1 is convenientpractically. On an anhydrous basis, the ratio of silica to collector canvary from about 0.06 to 0.6 part by weight of silica to 1 part by weightof collector. A satisfactory reagent also can be formed by mixing driedand ground silica gel with fatty acid type collector. If the premixedreagent is used promptly, it can have any pH value within the range ofabout 3 to 8, but it is more stable if acidified to a pH value of about3 to 6, preferably with sulphuric acid, although other equivalent acidswork just as well.

The reagent is then intimately mixed with a pulp of the ore containingabout 10 to 85 per cent solids by weight. The quantity of reagent canvary from 1 to 15 pounds of pre-mixed reagent per long ton of crude ore,or on an anhydrous basis, from about 0.5 to 5.0 pounds of collector andfrom about 0.2 to 3.0 pounds of silica per long ton of ore. For manyores I find about 4 to 5 pounds of the 1:1 pro-mixed reagent issatisfactory. In general an excess of colloidal silica would tend todepress iron oxide minerals and an excess of collector would tend tofloat silicious minerals. Conveniently at least part of the reagent canbe added to the pulp in the ballmill and the remainder in the flotationcell. Where the pulp is re-treated after the first flotation treatment,make-up reagent can be added as needed. Also it is apparent that thecollector and the colloidal silica can be introduced to the pulpseparately. If the silica gel first is dried, the grinding and mixingwith the collector conveniently can take place in the ball-mill, eitherwith or without ore present. The pulp pH can vary from about 5.5 to 7.5.As is usual in flotation processes, the optimum quantities of reagentwithin the foregoing ranges, the best mode of introducing the reagent,the optimum pulp pH and other operating conditions vary with differentores and should be determined by experiment in each instance.

In some instances it is desirable to introduce a small quantity of ahydrocarbon oil to modify the froth. I find that Bunker C fuel oil is aninexpensive and satisfactory hydrocarbon for the purpose, although manyequivalents are possible. Colloidal silica and fatty acid typecollectors produce a fast-forming dry froth which can mechanicallyentrap silicious particles and thus the float product may requireseveral re-treatments. By introducing hydrocarbon oil in an amountwithin the range of about 0.5 to 4.0 pounds per long ton of crude ore, Iproduce a froth which does not entrap undesired particles to nearly asgreat an extent.

To assist in describing the present invention, I have compiled thefollowing specific examples of treatments of ores in accordance with thein vention.

Example I The ore treated was Spruce taconite, which is representativeof a common type, and in this instance contained 34.8% iron and 48.6%silica. The iron minerals were chiefly hematite and goethite with aminor content of magnetite, and the gangue was chiefly quartz with aminor content of carbonates and iron silicates. Previously this ore hadnot been beneficiated satisfactorily with fatty acid type collectors.

A reagent was compounded by mixing 10 grains of colloidal silicasolution (about 30% S102) substantially free of ions of either alkalimetals or alkaline earth metals (Ludox) and 10 grams of oleic acid andagitating the mixture until it was emulsified. A sample of the ore wascrushed dry to pass a l-mesh screen and then ball-milled with water anda quantity of emulsion equivalent to 1 pound each of colloidal silicasolution (about 30% S102) and oleic acid per long ton of ore. The solidsin the milled pulp were minus 325 mesh.

The pulp was transferred to a small Denver flotation cell withadditional water and was treated by flotation in the usual way. No othermaterials were introduced, except make-up quantities of the reagentemulsion. The total reagent including that added to both the ball milland the flotation cell, was equivalent to two pounds each of colloidalsilica solution and oleic acid per long ton of ore. The float product orconcentrate was returned to the cell and re-cleaned four times. Theoriginal underflow and the first cleaner underflow were combined as atailing.

The second, third and fourth cleaner'underflows were combined as amiddling which might in actual operation be returned to the millcircuit.

The results were as follows:

Percent Analysis, Distribution,

It is to be noted that no conditioning agents of any kind were used inthe test. The pH of the flotation pulp was about 7.30, which isapproximately the same as the pH obtained on grinding the ore in waterin the absence of reagent.

Example II The ore treated was the same as in Example I and the reagentwas the same except that crude tall oil (Opoil) was substituted foroleic acid as the collector. A 500 gram sample of the ore was crusheddry to pass a i l-mesh screen and ball-milled for 25 minutes with 500ml. water and 50 drops of the reagent. The solids in the milled pulpwere 90.8% minus 325 mesh.

The milled pulp was transferred to a 500 gram Denver sub-A flotationcell with water and conditioned 3 minutes with 12 drops additionalreagent. The total reagent including that added to the mill wasequivalent to 2 pounds each of colloidal silica solution and tall oilper long ton of ore. lhe pulp was subjected to a flotation treatment fora seven minute period during which air admission to the cell wasregulated to avoid excessive froth volume. The concentrate was returnedto the cell and re-cleaned seven times with, small additions of thepre-mixed reagent and colloidal silica for the last four cleanings. Thetotal reagents for the entire test were equivalent to 3.3 pounds ofcollector and 4 pounds of colloidal silica solution per long ton of ore.

The results were as follows! Analysis his? Percent bution ProductPercent Percent gf Fe Insol.

Heads (calculated) 100.0 34. 53 100.0 Concentrate 48.1 (11.09 9.84 85.1Combined 'lalliugs 51.9 9.94 14.9

Example III The ore treated was the same asin Examples I and II. Theiron oxide minerals are about 90% freed from the gangue when the ore iscrushed to minus 150 mesh, but it has been the usual practice to grindthe ore finer than this for flotation with other reagent combinations.In the present example the ore was treated in a somewhat coarser state.

cell with water. A screen analysis on an identically prepared sample wasas follows:

pronounced ion exchange capacity.

example anionic combinations which employ soap, starch,lime and caustic.or cationic combinations which employ organic amines. Taconite orescommonly contain silicate and carbonate minerals that have highlyadsorptive properties, a tendency to slime on grinding, and Silicioussiderite is a typicalore componet of this sort. Previously it not onlyhas been impossible to obtain a satisfactory concentrate from silicioussiderite alone, but when silicious siderite is present with cleanerores, it prevents recovery of iron oxide. Whereas Spruce taconite usedin Examples I, II and III has a cation exchange capacity of 0.55milliequivalents per 100 grams by the ammonium acetate method (Bray) and0.46 mil liequivalent by a calcium chloride method, typicalcorresponding values for silicious siderite are 6.20 and 8.35milliequivalents per 100 grams. I have found that the ability oftaconites to be concerntrated diminishes greatly with increase in ionexchange capacity.

400 grams of taconite as used in the preceding examples and 100 grams ofsilicious siderite were crushed dry to pass a le-mesh screen andintroduced to a ball mill with 500 ml. of water and apre-mixed reagentemulsion which consisted of the equivalent of 2 pounds of tall oil, 2pounds of colloidal silica. solution (about SiOz) and 0.12 pounds ofoleic acid per long ton of ore. The mixture was milled for 15 minutesand the ore pulp transferred to a 500 gram Denver M h wt Cumummflotation cell with water. Flotation and re-cleanes Percent Percent ingwere-carried out in a fashion similar to Examples II and III. The totalreagent additions in eluding those made to the mill were equivalent to nf gj 2.67 pounds each of colloidal silica solution and Minus 325 2 191)tall oil and 0.13 pounds of oleic acid per long ton of ore. I Theflotation and re-cleaning were carried out 0 The results were asfollows:

Analysis Distribution r a t ro uct cell Per- Pcr- Percent Wt. Percentcont cent Units Fe Fe, Spruce Fe Insol. F9" Tmal 'Portion Totalcalculated heads 100.0 33.46 33. 4s Spruce ore content.. 80.0 35.0028.00 Concentrate... 40.2 save 10. 48 23.03 70.6 84.4 Combinedtailings.- 59.8 16.44 cs3 29.4 15.6 in the fashion as 1n Example II. Thetotal Example V reagent additions for the entire operation wereequivalent to 2.67 pounds each of collector and colloidal silicasolution per long ton of ore.

The results were as follows:

, Percent Analysis Distribution, duct Wt. percent Fe percent Fc Heads(calculated) 1'00. 0 35. 23 100.0 Concentrate 53. 7 (50. (ll 91. 6Combined 'lailings 46. 3 ll. 46 8. 4

Although the taconite used in Examples I, II and III had not previouslybeen treated successfully for recovery of the iron oxides withcollectors of the fatty acid type, it is considered a relatively cleantaconite andcan-be treatedsuccessfully with other known flotationmethodslor In practice the seven re-cleaning operations of Examples II,III and IV might prove disadvantageous. The need for such a. largenumber of re-cleaning operations is believed due to mechanicalentrapment of silicious mineral particles in the last-formin dry froth,which is characteristic of the flotation when only colloidal silica andthe fatty acid collector are used. In the present example a hydrocarbonoil is introduced as a froth modifier and substantially reduces thenumber of cleaning operations needed.

500 grams of taconite like that used in the preceding examples was drycrushed to passa 14-mesh screen and added to a ball mill with 500 ml.of. water and a reagent consisting of tall oil and colloidal silicasolution equivalent to 2 pounds of each per long ton of ore. The mixturewas milled for 15 minutes and the pulp transferred to a 500 gram Denverflotation cell with water. A hydrocarbon oil, in this instance BunkervC-fuel oil, was added to-the charge in the cell in an amount equivalentto Ob -pounds per long ton of ore. The mixture was condi- The resultswere as follows:

Percent Analysis, Distribution, Product Wt. percent Fe percent Fe Heads(calculated)... 100.0 34. 72 0.00 Concentrate 48. 6 60. 4. 04 Middling7. 9 28. 31 6. 45 Tailing 43. 5 7. 59 9. 51

From the foregoing description it is [seen that the present inventionprovides flotation methods and reagents which utilize only inexpensivematerials and yet furnish better separations of iron oxide minerals fromsilicious minerals than methods and reagents =previ0usly known. Aspreviously suggested, it is of the essence of the invention that thereagents be substantially free of alkali metal ions, that is, that theyhave a mol ratio of silica to alkali metals of at least 25 to 1. Oncethis condition is met, a wide choice of inexpensive collectors andcolloidal silica can be used. While I have described in detail onlycertain preferred modes of carrying out the invention and certainpreferred reagent compositions, it is apparent modifications may arise.Therefore I do not wish to be limited to this disclosure, but only tothe scope of the appended claims. e

1. A method for floating iron oxide minerals from silicious mineralscomprising adding to an ore pulp, which contains about to 85% solids byweight, about 0.5 to 5.0 pounds of a collector of the fatty acid typeper long ton of solids in the pulp and about 0.2 to 3.0 pounds ofcolloidal silica on an anhydrous basis per long ton of solids, thecollector being of the group which consists of higher fatty acids,esters of the higher fatty acids, resin acids, naphthenic acids andmixtures of the foregoing, but being substantially free of alkali metalions the colloidal silica having mol ratio of silica to alkali metals ofat least 25 to 1, and subjecting the pulp to a flotation treatment.

2. A method for beneficiating low grade iron ores comprising adding toan ore pulp which contains about 10 to 85% solids by weight, about 0.5to 5.0 pounds of a collector of the fatty acid type per long ton ofsolids in the pulp and about 0.2 to 3.0 pounds of colloidal silica on ananhydrous basis per long ton of solids, the collector being of the groupwhich consists of higher fattyacids, esters of the higher fatty acids,resin acids, naphthenic acids and mixtures of the foregoing, but beingsubstantially free of alkali metal ions, the colloidal silica having amol ratio of silica to alkali metals of at least 25 to 1, and subjectingthe pulp to a flotation treatment which floats the iron oxide minerals.

3. A method for beneflciating low grade iron ores comprising adding toan ore pulp which contains about 10 to 85% solids by weight, about 0.5to 5.0 pounds of a collector of the fatty acid type per long ton ofsolids in the pulp, about 0.2 to 3.0 pounds of colloidal silica on ananhydrous basis per long ton of solids, and about 0.5 to 4.0 pounds of ahydrocarbon oil per-long ton of solids, the collector being offfthegroupwliich consists of higher fatty acids, esters of thehigher fattyacids, resin-acids, naphthenic acids and mixtures of the foregoing, butbeing substantially free of alkali metal ions, the colloidal silicahaving a mol ratio of silica to alkali metals of at least 25 to 1, andsubjecting the pulp to a flotation treatment which floats the iron oxideminerals.

4. A pre-mixed flotation reagent consisting of an aqueous emulsion of acollector of the fatty acid type and colloidal silica which has a molratio of silica to alkali metals of at least 25 to 1, the collectorbeing of the group which consists of higher fatty acids, esters of thehigher fatty acids, resinacids, naphthenic acids and-mixtures of theforegoing, but being substantially free of alkali metal ions, the ratioof colloidal silica to collector on an anhydrous basis being from about0.06 to 0.6 part by weight of silica to 1 part by weight of collector.

5. A pre-mixed flotation reagent consisting of an aqueous emulsion of acollector of the fatty acid type and colloidal silica which has a molratio of silica to alkali metals of at least 25 to l, the collectorbeing of the group which consists of higher fatty acids, esters of thehigher fatty acids, resin acids, naphthenic acids and mixtures of theforegoing, but being. substantially free of alkali metal ions, saidcolloidal silica acting as the emulsifying agent, the ratio of colloidalsilica to collector on an anhydrous basis being from about 0.06 to 0.6part by weight of silica to 1 part by weight of collector, the emulsionbeing acidified to a pH value of about 3 to 6.

6. A method for floating iron oxide minerals from silicious mineralscomprising addin toan ore pulp, which contains about 10 to 85% solids byweight, a pre-mixed reagent consisting of an aqueous emulsion of acollector of the fatty acid type and colloidal silica which has a molratio of silica to alkali metals of at least 25 to 1, the collectorbeing of the group which consists of higher fatty acids, esters of thehigher fatty acids, resin acids, naphthenic acids and mixtures of theforegoing, but being substantially free of alkali metal ions, thequantity of collector being about 0.5 to 5.0 pounds per long ton ofsolids in the pulp and the quantity of colloidal silica being about 0.2to 3.0 pounds per long ton of solids on an anhydrous basis, andsubjecting the pulp to a flotation treatment.

7. A method for floating iron oxide minerals from silicious mineralscomprising adding to a coarse ore pulp, which contains 10 to solids byweight, about 0.5 to 5.0 pounds of a collector of the fatty acid typeper long ton of solids in the pulp and about 0.2 to 3.0 pounds of driedsilica gel per long ton of solids, the collector being of the groupwhich consists of higher fatty acids, esters of the higher fatty acids,resin acids, naphthenic acids and mixtures of the foregoing, but beingsubstantially free of alkali metal ions, the silica gel having a molratio of silica to alkali metals of at least 25 to 1, grinding andmixing the pulp, collector and silica gel, and subjecting the resultingground and mixed pulp to a flotation treatment FREDERICK R. ARCHIBALD.

References Cited in the flle of this arent I UNITED STATES PATENTSNumber Name Date 1,326,855 Edser et al. Dec. 30, 1919 I 1,492,904 Sulmanet al. May 6, 1924 2,164,063 I-Iandy June 27, 1939 2,470,150 De VaneyMay 17, .1949

1. A METHOD FOR FLOATING IRON OXIDE MINERALS FROM SILICIOUS MINERALSCOMPRISING ADDING TO AN ORE PULP, WHICH CONTAINS ABOUT 10 TO 85% SOLIDSBY WEIGHT, ABOUT 0.5 TO 5.0 POUNDS OF A COLLECTOR OF THE FATTY ACID TYPEPER LONG TON OF SOLIDS IN THE PULP AND ABOUT 0.2 TO 3.0 POUNDS OFCOLLOIDAL SILICA ON AN ANHYDROUS BASIS PER LONG TON OF SOLIDS, THECOLLECTOR BEING OF THE GROUP WHICH CONSISTS OF HIGHER FATTY ACIDS,ESTERS OF THE HIGHER FATTY ACIDS, RESIN ACIDS, NAPHTHENIC ACIDS ANDMIXTURES OF THE FOREGOING, BUT BEING SUBSTANTIALLY FREE OF ALKALI METALIONS THE COLLOIDAL SILICA HAVING A MOL RATIO OF SILICA TO ALKALI METALSOF AT LEAST 25 TO 1, AND SUBJECTING THE PULP TO A FLOATION TREATMENT.